1. Field of the Invention
The present invention relates to image formation materials for use in electrophotography, electrostatic recording and ink jet printing method, and an image fading prevention method by use of the image formation materials, and more particularly to a toner or developer for use in electrostatic development and a color image fading prevention method using the toner or developer.
2. Discussion of Background
In accordance with recent development of office automation (OA), excellent image formation method, particularly color image formation method, is demanded.
As image formation methods, for instance, electrophotography, electrostatic recording method, and ink jet printing method are currently employed.
For example, in electrophotography, latent electrostatic images are formed on a photoconductor which comprises a photoconductive material, the latent electrostatic images are then developed to toner images by a developer, and when necessary, the toner images are transferred to a transfer sheet or the like, and fixed thereto by the application of heat or pressure thereto, whereby visible images are formed thereon.
Multicolor images are obtained by exposing such a photoconductor to light images through a color separation filter, or exposing the photoconductor to images read by a scanner for writing the images in the photoconductor, to form latent electrostatic images. The thus formed latent electrostatic images are developed by use of color developers of yellow, magenta, cyan and black, and yellow, magenta, cyan and black toner images are superimposed, whereby multicolor images can be obtained.
Conventional toners for use in electrophotography are produced by kneading a thermoplastic resin, a pigment, and a charge controlling agent, and pulverizing the kneaded mixture. In the thus produced toner are dispersed particles of the pigment, and therefore light scattering is caused by the dispersed pigment particles, so that the transparency of the toner is lowered. Therefore, when color images are formed by use of a plurality of such toners, the color reproduction thereof is poor. Color images formed by such toners, when produced on a transparent sheet for overhead projector (OHP), have the shortcoming that projected images are dark and the chroma thereof is low.
In order to improve the transparency of such color images, it has been proposed that C.I. Solvent Blue 35, indophenol, and anthraguinone dye be employed instead of pigments, as disclosed In Japanese Laid-Open Patent Applications 62-273570, 64-29855, and 1-284865. Toners comprising such dyes, however, have the shortcoming that the light resistance or fading resistance thereof is so poor that they cannot be used in practice.
In order to improve the light resistance or fading resistance of such toners, it has been proposed to contain an ultraviolet absorbing agent or an anti-oxidizing agent in such toners as disclosed in Japanese Laid-Open Patent Applications 52-12838, 53-370925, 60-93453, 1-172973, 1-172974, 1-172975, 1-172976, 2-264964, 2-264965, and 2-264966.
However, toners containing an ultraviolet absorbing agent or an anti-oxidizing agent are not capable of exhibiting a sufficient fading resistance for use in practice, while maintaining satisfactory spectral reflection characteristics. Image formation materials for forming color images by ink jet printing method and other methods also have the same problems as mentioned above.